This application relates generally to fiber-optic communications and more specifically to techniques and devices for providing a survivable transmission architecture.
The Internet and data communications are causing an explosion in the global demand for bandwidth. Fiber optic telecommunications systems are currently deploying a relatively new technology called dense wavelength division multiplexing (DWDM) to expand the capacity of new and existing optical fiber systems to help satisfy this demand. In DWDM, multiple wavelengths of light simultaneously transport information through a single optical fiber. Each wavelength operates as an individual channel carrying data. The carrying capacity of a fiber is multiplied by the number of DWDM channels used. Today, DWDM systems employing up to 160 channels are available from multiple manufacturers, with more promised in the future.
In all telecommunication networks, there is the need to connect individual channels or circuits to individual destination points, such as an end customer or to another network. Systems that perform these functions are called cross-connects. Additionally, there is the need to add or drop particular channels at an intermediate point. Systems that perform these functions are called add-drop multiplexers (ADMs). All of these networking functions are currently performed by electronics—typically an electronic synchronous optical network (“SONET”) or synchronous digital hierarchy (“SDH”) system. However, SONET/SDH systems are designed to process only a single optical channel. Multiple-wavelength systems would require multiple SONET/SDH systems operating in parallel to process the many optical channels. This makes it difficult and expensive to scale DWDM networks using SONET/SDH technology.
The alternative is an all-optical network. Optical networks designed to operate at the wavelength level are commonly called “wavelength routing networks” or “optical transport networks” (OTNs). In a wavelength routing network, the individual wavelengths in a DWDM fiber must be manageable. New types of photonic network elements operating at the wavelength level are required to perform the cross-connect, ADM, and other switching functions. Two of the primary functions are optical add-drop multiplexers (OADM) and wavelength-selective cross-connects (WSXC).
Optical networks are typically configured in the form of rings, with a plurality of nodes that include network elements, such as optical equipment, electrical equipment, etc. It is generally desirable to provide a scheme with the network to protect traffic in the event that one of the nodes or fiber connections becomes disabled. Various schemes that provide traffic protection have been used, but generally ring transmission systems have been configured for only a specific protection scheme. Such an approach includes inherent limitations in both efficiency and flexibility. There is a general desire and need in the art for protection schemes that can improve this efficiency and flexibility.